Since many people don't use the Linux networking code at all until
they get a PPP link, this section describes generally what's needed to
get things running. In principle none of this is special to PPP. For
more details, you should consult the relevant Linux HOWTOs. If you
already understand network setup, you can skip this section.

The first file that requires attention is the rc script that does
network configuration at boot time, called /etc/rc.net or
/etc/rc.d/rc.net.{1,2} or something similar, depending on
your Linux distribution. This file should ifconfig the loopback
interface lo, and should add an interface route for it. These lines
might look something like this:

$CONFIG lo 127.0.0.1
$ROUTE add loopback

or

/sbin/ifconfig lo 127.0.0.1
/sbin/route add 127.0.0.1

However, it should not config an ethernet card or install
any other routes (unless you actually have an ethernet card, in which
case I'll assume you know what to do). Many distributions will
provide scripts that expect you to have an ethernet card.